Media having properties not found in nature can be artificially composed by arranging small pieces of metal, dielectric, magnetic substance, superconducting substance and the like at sufficiently short intervals relative to the wavelength (about 1/10 of the wavelength or less). Such media are known as metamaterials in the sense that they surpass media available from nature. Whereas the properties of metamaterials vary in many different ways according to the shape and material of unit particles and their arrangement, metamaterials whose equivalent permittivity ε and permeability μ become negative at the same time in particular are named “left-handed materials” as their electric field, magnetic field and wave vector constitute a left-handed system. As opposed to them, conventional materials whose equivalent permittivity ε and permeability μ become positive at the same time are called “right-handed materials”. The regions of relationship among these permittivity ε, permeability μ and media can be classified into media of the first through fourth quadrants according to the positiveness/negativeness of permittivity ε and that of permeability μ as shown in FIG. 1.
In particular, “left-handed materials” have peculiar features including the presence of waves whose signs of group velocity (the velocity at which energy propagates) and phase velocity (the velocity at which phase proceeds) are inverted, known as backward waves, and the amplification of the evanescent wave, which is a wave exponentially attenuating in the non-propagating region.
The surface waves are known to propagate on the boundary between media which are not metamaterials (naturally continuous media) but the sign of whose permittivity ε is negative (negative permittivity media) and those the sign of whose permittivity ε is positive (positive permittivity media). For instance, as revealed in H. Raether, “Surface plasmons on smooth and rough surfaces and on gratings,” Springer-Verlag, 1988” (Reference 1), the permittivity of metal in the optical region is negative, and surface waves known as surface plasmons are present on the boundary between air and dielectrics, whose permittivity is positive.
By contrast, surface waves are also present on the boundary between media the sign of whose permeability μ is negative (negative permeability media) and those the sign of whose permeability μ is positive (positive permeability media). As disclosed in B. Lax and K J Button, “Microwave Ferrite and Ferrimagnetics,” McGraw-Hill, 1962 (Reference 2), it is known that the equivalent permeability of magnetized ferrite becomes negative in the high frequency region, and surface waves propagate on the boundary between them and air or dielectrics, whose permeability is positive.
Thus, surface waves propagate on the boundary between media the sign of whose permittivity ε or permeability μ is negative and those the sign of whose permittivity ε and permeability μ are both positive. In particular, a state in which surface waves propagate on the boundary between media the sign of whose permeability μ is negative and media the sign of whose permeability μ is positive is shown in FIG. 2.
However, the negative permittivity characteristic of metal in the optical region and the negative permeability characteristic of magnetized ferrite are the intrinsic properties of materials available from nature, and neither their permittivity ε nor permeability μ can be designed as desired. Therefore, the surface wave propagation frequency band, which is determined by these characteristics, can neither be determined nor designed as desired. For instance, whereas surface plasmons attributable to the negative permittivity characteristic of metal constitute a phenomenon in the optical region, and the transmission band of the surface magnetostatic wave of ferrite is determined by the direction and magnitude of the applied D.C. magnetic field, even if the D.C. magnetic field of a realistic number T (Tesla) is added, the microwave region will be the upper limit. Nor is there any easy way to excite these surface plasmons or surface magnetostatic wave.